DIAGNOSIS OF VIRAL INFECTION

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DIAGNOSIS OF VIRAL INFECTION
An Overview
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Diagnostic Methods in Virology

• 1. Direct Examination
• 2. Indirect Examination (Virus Isolation)
• 3. Serology

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Direct Examination

• 1. Antigen Detection immunofluorescence,
  ELISA etc.
• 2. Electron Microscopy morphology of
  virus particles
• immune electron
  microscopy
• 3. Light Microscopy histological
  appearance
• inclusion bodies
• 4. Viral Genome Detection hybridization with
  specific nucleic acid probes
  polymerase chain
  reaction (PCR)

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Indirect Examination

• 1. Cell Culture cytopathic effect (CPE)
• haemabsorption
• immunofluorescence
• 2. Eggs pocks on CAM
• haemagglutination
• inclusion bodies
• 3. Animals disease or death

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Serology

• Detection of rising titers of antibody between
  acute and convalescent stages of infection, or
  the detection of IgM in primary infection.

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Virus Isolation

• Cell Cultures are most widely used for virus
  isolation, there are 3 types of cell cultures
• 1. Primary cells - Monkey Kidney
• 2. Semi-continuous cells - Human embryonic kidney
  and skin fibroblasts
• 3. Continuous cells - HeLa, Vero, Hep2, LLC-MK2,
  MDCK
• Primary cell culture are widely acknowledged as
  the best cell culture systems available since
  they support the widest range of viruses.
  However, they are very expensive and it is often
  difficult to obtain a reliable supply. Continuous
  cells are the most easy to handle but the range
  of viruses supported is often limited.

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Cell Cultures

• Growing virus may produce
• 1. Cytopathic Effect (CPE) - such as the
  ballooning of cells or syncytia formation, may be
  specific or non-specific.
• 2. Haemadsorption - cells acquire the ability to
  stick to mammalian red blood cells.
• Confirmation of the identity of the virus may be
  carried out using neutralization,
  haemadsorption-inhibition or immunofluorescence
  tests.

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Cytopathic Effect (1)
Cytopathic effect of enterovirus 71 and HSV in
cell culture note the ballooning of cells.
(Virology Laboratory, Yale-New Haven Hospital,
Linda Stannard, University of Cape Town)
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Cytopathic Effect (2)
Syncytium formation in cell culture caused by
Resp. Syncytial Virus (top), and measles virus
(bottom). (courtesy of Linda Stannard,
University of Cape Town, S.A.)
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Haemadsorption
Syncytial formation caused by mumps virus and
haemadsorption of erythrocytes onto the surface
of the cell sheet. (courtesy of Linda Stannard,
University of Cape Town, S.A.)
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Problems with cell culture

• Long period (up to 4 weeks) required for result.
• Often very poor sensitivity, sensitivity depends
  on a large extent on the condition of the
  specimen.
• Susceptible to bacterial contamination.
• Susceptible to toxic substances which may be
  present in the specimen.
• Many viruses will not grow in cell culture e.g.
  Hepatitis B, Diarrhoeal viruses, parvovirus,
  papillomavirus.

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Rapid Culture Techniques

• Rapid culture techniques are available whereby
  viral antigens are detected 2 to 4 days after
  inoculation. The CMV DEAFF (Detection of Early
  Antigen Fluorescent Foci) test is the best
  example, whereby
• The cell sheet is grown on individual cover slips
  in a plastic bottle.
• Following inoculation, the bottle then is spun at
  a low speed for one hour (to speed up the
  adsorption of the virus) and then incubated for 2
  to 4 days.
• The cover slip is then taken out and examined for
  the presence of CMV early antigens by
  immunofluorescence.

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DEAFF test for CMV
(Virology Laboratory, Yale-New Haven Hospital)
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Viruses Isolated by Cell Culture
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Electron Microscopy

• 106 virus particles per ml required for
  visualization, ? 50,000 - 60,000 magnification
  normally used. Viruses may be detected in the
  following specimens.
• Faeces Rotavirus, Adenovirus
• Norwalk like viruses
• Astrovirus, Calicivirus
• Vesicle Fluid HSV
• VZV
• Skin scrapings papillomavirus, orf
• molluscum contagiosum

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Electronmicrographs
Rotavirus
Astroviruses
Adenovirus
(courtesy of Linda Stannard, University of Cape
Town, S.A.)
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Immune Electron Microscopy

• The sensitivity and specificity of EM may be
  enhanced by immune electron microscopy. There are
  two variants-
• Classical Immune electron microscopy (IEM) - the
  sample is treated with specific anti-sera before
  being put up for EM. Viral particles present will
  be agglutinated and thus congregate together by
  the antibody.
• Solid phase immune electron microscopy (SPIEM) -
  the grid is coated with specific anti-sera. Virus
  particles present in the sample will be absorbed
  onto the grid by the antibody.

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Problems with Electron Microscopy

• Expensive equipment
• Expensive maintenance
• Require experienced observer
• Sensitivity often low

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Serology

• Criteria for diagnosing Primary Infection
• 4 fold or more increase in titre of IgG or total
  antibody between acute and convalescent sera
• Presence of IgM
• Seroconversion
• A single high titre of IgG (or total antibody) -
  very unreliable
• Criteria for diagnosing Reinfection
• fold or more increase in titre of IgG or total
  antibody between acute and convalescent sera
• Absence or slight increase in IgM

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Typical Serological Profile After Acute Infection

• Note that during reinfection, IgM may be absent
  or present at a low level transiently

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Complement Fixation Test
Complement Fixation Test in Microtiter Plate.
Rows 1 and 2 exhibit complement fixation obtained
with acute and convalescent phase serum
specimens, respectively. (2-fold serum dilutions
were used)
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ELISA for HIV antibody

• Microplate ELISA for HIV antibody colored wells
  indicate reactivity

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Western Blot

• HIV-1 Western Blot
• Lane1 Positive Control
• Lane 2 Negative Control
• Sample A Negative
• Sample B Indeterminate
• Sample C Positive

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Usefulness of Serological Results

• How useful a serological result is depends on the
  individual virus.
• For example, for viruses such as rubella and
  hepatitis A, the onset of clinical symptoms
  coincide with the development of antibodies. The
  detection of IgM or rising titres of IgG in the
  serum of the patient would indicate active
  disease.
• However, many viruses often produce clinical
  disease before the appearance of antibodies such
  as respiratory and diarrhoeal viruses. So in this
  case, any serological diagnosis would be
  retrospective and therefore will not be that
  useful.
• There are also viruses which produce clinical
  disease months or years after seroconversion e.g.
  HIV and rabies. In the case of these viruses, the
  mere presence of antibody is sufficient to make a
  definitive diagnosis.

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Problems with Serology

• Long period of time required for diagnosis for
  paired acute and convalescent sera.
• Mild local infections such as HSV genitalis may
  not produce a detectable humoral immune response.
• Extensive antigenic cross-reactivity between
  related viruses e.g. HSV and VZV, Japanese B
  encephalitis and Dengue, may lead to false
  positive results.
• immunocompromised patients often give a reduced
  or absent humoral immune response.
• Patients with infectious mononucleosis and those
  with connective tissue diseases such as SLE may
  react non-specifically giving a false positive
  result.
• Patients given blood or blood products may give a
  false positive result due to the transfer of
  antibody.

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CSF antibodies

• Used mainly for the diagnosis of herpes simplex
  and VZV encephalitis
• CSF normally contain little or no antibodies
• presence of antibodies suggest meningitis or
• meningoencephalitis

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Rapid Diagnosis Based on the Detection of Viral
Antigens

• Nasopharyngeal Aspirate RSV
• Influenza A and B
• Parainfluenza
• Adenovirus
• Faeces Rotaviruses
• Adenoviruses
• Astrovirus
• Skin HSV
• VZV
• Blood CMV (pp65 antigenaemia test)

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Immunofluorescense
Positive immunofluorescence test for rabies virus
antigen. (Source CDC)
(Virology Laboratory, Yale-New Haven Hospital)
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CMV pp65 antigenaemia test
(Virology Laboratory, Yale-New Haven Hospital)
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Advantages and Disadvantages

• Advantages
• Result available quickly, usually within a few
  hours.
• Potential Problems
• Often very much reduced sensitivity compared to
  cell culture, can be as low as 20. Specificity
  often poor as well.
• Requires good specimens.
• The procedures involved are often tedious and
  time-consuming and thus expensive in terms of
  laboratory time.

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Specimens for Routine Tests
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Molecular Methods

• Methods based on the detection of viral genome
  are also commonly known as molecular methods. It
  is often said that molecular methods is the
  future direction of viral diagnosis.
• However in practice, although the use of these
  methods is indeed increasing, the role played by
  molecular methods in a routine diagnostic virus
  laboratory is still small compared to
  conventional methods.
• It is certain though that the role of molecular
  methods will increase rapidly in the near future.

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Classical Molecular Techniques

• Dot-blot, Southern blot are examples of classical
  techniques. They depend on the use of specific
  DNA/RNA probes for hybridization.
• The specificity of the reaction depends on the
  conditions used for hybridization. However, the
  sensitivity of these techniques is not better
  than conventional viral diagnostic methods.
• However, since they are usually more tedious and
  expensive than conventional techniques, they
  never found widespread acceptance.

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Polymerase Chain Reaction (1)

• PCR allows the in vitro amplification of specific
  target DNA sequences by a factor of 106 and is
  thus an extremely sensitive technique.
• It is based on an enzymatic reaction involving
  the use of synthetic oligonucleotides flanking
  the target nucleic sequence of interest.
• These oligonucleotides act as primers for the
  thermostable Taq polymerase. Repeated cycles
  (usually 25 to 40) of denaturation of the
  template DNA (at 94oC), annealing of primers to
  their complementary sequences (50oC), and
  primer extension (72oC) result in the exponential
  production of the specific target fragment.
• Further sensitivity and specificity may be
  obtained by the nested PCR.
• Detection and identification of the PCR product
  is usually carried out by agarose gel
  electrophoresis, hybridization with a specific
  oligonucleotide probe, restriction enzyme
  analysis, or DNA sequencing.

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Polymerase Chain Reaction (2)

• Advantages of PCR
• Extremely high sensitivity, may detect down to
  one viral genome per sample volume
• Easy to set up
• Fast turnaround time
• Disadvantages of PCR
• Extremely liable to contamination
• High degree of operator skill required
• Not easy to set up a quantitative assay.
• A positive result may be difficult to interpret,
  especially with latent viruses such as CMV, where
  any seropositive person will have virus present
  in their blood irrespective whether they have
  disease or not.
• Very expensive.

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Schematic of PCR
Each cycle doubles the copy number of the target
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Other Newer Molecular Techniques

• Branched DNA is essentially a sensitive
  hybridization technique which involves linear
  amplification. Whereas exponential amplification
  occurs in PCR.
• Therefore, the sensitivity of bDNA lies between
  classical amplification techniques and PCR. Other
  Newer molecular techniques depend on some form of
  amplification.
• Commercial proprietary techniques such as LCR
  (ligase chain reaction), NASBA (Nucleic Acid
  Sequence Based Amplification) , TMA (Tissue Micro
  Arrays) depend on exponential amplification of
  the signal or the target.
• Therefore, these techniques are as susceptible to
  contamination as PCR and share the same
  advantages and disadvantages.
• PCR and related techniques are bound to play an
  increasingly important role in the diagnosis of
  viral infections.
• DNA chip is another promising technology where it
  would be possible to detect a large number of
  viruses, their pathogenic potential, and their
  drug sensitivity at the same time.

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Comparison between PCR and other nucleic acid
Amplification Techniques